Housing
What size is your tank? 42gallons
What temperature is your tank? 27 Celcius
Does your tank have a filter? Yes
Does your tank have an air stone or other type of aeration? No
Is your tank heated? Yes
What tank mates does your betta fish live with? Cory Dora Catfish, Neon and Glowlight Tetras

Food
What type of food do you feed your betta fish? Bloodworms; freeze dried
How often do you feed your betta fish? 2-3 worms per day

Maintenance
How often do you perform a water change? Every 2 weeks
What percentage of the water do you change when you perform a water change? 50%
What type of additives do you add to the water when you perform a water change? Stress Zyme, Stress Coat +

Water Parameters:
Have you tested your water? If so, what are the following parameters?

Symptoms and Treatment
How has your betta fish's appearance changed? Weird "mold" looking growth on tail fin, slightly paler than normal (that could be me over reacting as I'm very loving towards him)
How has your betta fish's behavior changed? Less active
When did you start noticing the symptoms? Noticed small growth this morning, has probably quadrippled in size over the last 12 hours.
Have you started treating your fish? If so, how? I have isolated him into a 5gal heated tank at 28 degrees Celcius. I cannot buy medice till tomorrow evening, unsure of what to buy.
Does your fish have any history of being ill? Had a white spot on his head and was very lazy when another fish in the tank died.
How old is your fish (approximately)? 1 1/2 years.

Thanks in advance, I'm wondering how I should treat it, hes had fin rot before... this looks more like a fungal growth, unfortunately I can't get pictures of it right now because its 1am where I live.

I've started him on Aquarium salt and Pimafix. It actually looks like the fungus has chewed out part of his tail and its literally hanging by the thread. :( Hes also lieing on his side, and will only come up if I tempt him with food.

Isolate him if possible to reduce stress. You can put him in a plastic container and float it in the tank to keep him warm. I assume the salt concentration is at 1tsp/gal. Up that to 2tsp/gal and perform daily 100% water changes. Use the higher dose on the Stress Coat for stress reduce and skin repair. Stop the Pimafix, it is harmful for bettas. The ingredients harm their labyrinth organs. If you can, get Maracyn I and II (@petsmart) OR API Fungus Cure (@petsmart) OR Jungle's Fungus Clear (@walmart). If you can lower the temp to 76*F-78*F that will help.

If you can get us a picture that would help us identify his illness better to make sure you get the med that would be most effective. Good luck and keep us posted!